1. Field of the Invention
This disclosed subject matter is generally related to field-responsive fluids, and more particularly to magnetorheological fluids with enhanced properties such as maintaining a highly viscous state after removal of a magnetic field.
2. Background of the Invention
Traditional magnetorheological fluids typically comprise magnetizable particles suspended in a base fluid. In the absence of a magnetic field, the magnetorheological fluids behave similar to a Newtonian fluid. However, in the presence of a magnetic field the particles acquire magnetic moments leading to interparticle forces between the particles. As a result of this interaction, the particles form chains and chain-like microstructures within the fluid that change the bulk rheological properties of the fluid. These chains are roughly parallel to the magnetic lines of flux associated with the field. Further, the magnetic field causes the fluid to enter a semi-solid state. This semi-solid state exhibits an increased resistance to shear. Resistance to shear is increased due to the magnetic attraction between particles of the chains. Adjacent chains of particles combine to form a wall which resists shear in the form of wall drag or fluid flow. The effect induced by the magnetic field is both reversible and repeatable for traditional magnetorheological fluids.
Hydrocarbons (oil, condensate and gas) are typically produced from wells that are drilled into the formation containing them. For a variety of reasons, such as inherently low permeability of the reservoirs or damage to the formation caused by drilling and completion of the well, the flow of hydrocarbons into the well may be undesirably low. In this case, the well is “stimulated” for example using hydraulic fracturing, chemical stimulation or a combination of the two.
Hydraulic fracturing involves injecting fluids into a formation at high pressure and rates such that the reservoir rock fails and forms a fracture (or fracture network), greatly increasing the surface area through which fluids may flow into the well. The number of horizontally drilled wells has continued to increase in the past few years and the need to maximize wellbore contact with the reservoir pose challenges in fracturing applications, especially in gas shale reservoirs. Shale beds are notoriously low permeability rocks, which means in general they need a hydraulic fracture stimulation to be economical.
When hydraulic fracturing or chemical stimulation stimulates multiple hydrocarbon-bearing zones, it is desirable to treat the multiple zones in multiple stages. In multiple zone fracturing, a first zone is fractured. After a first zone is fractured, the fracturing fluid is diverted to the next stage to fracture the next zone. This process is repeated until all zones are fractured. Alternatively, several zones may be fractured at one time, if they are closely located with similar properties. There are a number of methods for stress/pressure diversion in multiple fracturing stages e.g., bridge plug. Efforts are ongoing to find a cost-effective and controllable solution to enable multi-stage fracturing using diversion. In shale gas applications, maximizing reservoir contact through multi-stage fracturing is advantageous as this technique provides a cost-effective means of contacting the reservoir by creating large fractures. One of the main challenges in many tool-free multi-fracturing techniques is controllability of the fracturing process. Time dependency of the multi-stage fracturing process can be improved if an operator has the capability of controlling the processes.
The presently disclosed subject matter addresses the problems of the prior art by addressing controllability concerns in multi-fracturing applications.